Have you ever put you ear close to the structures (e.g. walls or floors) to hear better vibrations in the structure ?
Why do you hear more in this case when you close to the structure?

Answer to this question is hopefully given in this animation.An infinite plate vibrates with a standing pattern or a propagating pattern on its surface.
Depending on the ratio between the wavelength on the plate and the wavelength in the surrounding medium (e.g. air), the plate radiates with different efficiency.

Keywords:

	standing or propagating wave
      near field
      radiation efficiency
 
